1. Field of the Invention
The present invention relates to a semiconductor device having a structure in which a semiconductor chip is joined to a wiring board in a film shape, for example.
2. Description of Related Art
In order to reduce the mounting area of a semiconductor device, a chip size package which is an IC package of approximately the same size as the size of a semiconductor chip itself has been conventionally developed. One form of a chip size package (CSP) type semiconductor device is a surface mount type package. In the surface mount type package, a thinned semiconductor chip is joined to a film-shaped wiring board, and the film-shaped wiring board is mounted on a mounting board in electronic equipment. The wiring board joined to the semiconductor chip has an internal wiring connected to solder balls arranged in a two-dimensional manner on a lower surface of the wiring board by rewiring a plurality of pads arranged at a peripheral edge of the semiconductor chip.
In the above-mentioned construction, however, the significantly thinned semiconductor chip is joined to the wiring board having a different coefficient of thermal expansion therefrom. Accordingly, the package warps as the environmental temperature changes.
An object of the present invention is to provide a semiconductor device which can be prevented from warping, although it has a structure in which a thinned semiconductor chip is joined to a wiring board.
A semiconductor device according to the present invention comprises a semiconductor chip, a wiring board jointed to one surface of the semiconductor chip and electrically connected to the semiconductor chip, and a warp preventing board jointed to the other surface of the semiconductor chip and composed of the same material as that of the wiring board.
According to the present invention, the semiconductor chip is interposed between the wiring board and the warp preventing board which are composed of the same material (an insulating material, for example). Even if the semiconductor chip is thinned one having a thickness of approximately 100 xcexcm, therefore, a package may not warp due to the change in the environmental temperature. That is, when the environmental temperature changes, thermal expansion or thermal contraction equally occur on both surfaces of the semiconductor chip, thereby making it possible to prevent the package from warping.
It is preferable that an external connection member for surface mounting is arranged on a surface, facing away from the semiconductor chip, of the wiring board.
By this construction, the external connection member (a solder ball, a land, etc.) is provided on the surface, facing away from the semiconductor chip, of the wiring board. Accordingly, the semiconductor device can be surface-mounted on a mounting board in electronic equipment.
It is preferable that the warp preventing board is another wiring board, another semiconductor chip electrically connected to the warp preventing board being joined to a surface, facing away from the semiconductor chip, of the warp preventing board.
By this construction, the other semiconductor chip can be further stacked on the semiconductor chip with the warp preventing board interposed therebetween. Therefore, so-called three-dimensional mounting of the semiconductor chips is possible. Consequently, high-density mounting of the semiconductor chips is possible. As a result, it is possible to improve the substantial integration degree of the semiconductor device.
It is preferable that a wiring material for electrically connecting the wiring board and the warp preventing board is interposed therebetween.
By this construction, the connecting member for electrical connection is arranged between the wiring board and the warp preventing board. Accordingly, the other semiconductor chip joined to the warp preventing board (having the function of a wiring board) can be electrically connected to the wiring board.
Similarly, a warp preventing board composed of the same material as that of the wiring board is arranged on an upper surface of the other semiconductor chip, thereby making it possible to also construct a three-dimensional stacked structure comprising three or more layers. In this case, it is preferable that a wiring material is arranged between the wiring board and the warp preventing board and among the warp preventing boards in the respective layers. Consequently, it is possible to achieve an electrical connection among the semiconductor chips in the respective layers and/or between the semiconductor chip in each of the layers and the wiring board.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.